1. Field of the Invention
The present invention relates, in general, to an axial flow fan with a motor for electronic appliances, such as office or domestic electronic appliances, and, more particularly, to an axial flow fan with a BLDC(Brushless Direct Current) motor, the axial flow fan being optimally designed in diameter ratio, the number of blades, camber ratio, pitch angle and sweep angle, thus being reduced in operational noise in addition to being increased in air volume.
2. Description of the Prior Art
FIGS. 1a and 1b are plan and side views of a conventional axial flow fan integrated with a motor. FIG. 2 is a sectional view of the conventional axial flow fan taken along the line Axe2x80x94A of FIG. 1a. FIG. 3 is a sectional view of an electromagnetic induction-heating cooker provided with the conventional axial flow fan.
As shown in FIGS. 1a to 2, the typical size of a conventional axial flow fan is set to 92 mm(W)xc3x9792 mm (D)xc3x9725 mm(H). Such a conventional axial flow fan comprises a fan housing 7, with a motor 1 being firmly set within the housing 7. A hub 3 is firmly mounted to the rotating shaft 2 of the motor 1, with a plurality of blades 5 regularly fixed around the hub 3. The fan housing 7 covers the blades 5 so as to protect the blades 5 from external impact.
In such conventional axial flow fans, the motor 1 is typically selected from small-sized BLDC motors. The above axial flow fan also typically has seven blades 5. In the conventional axial flow fan, the axial height of the blades 5 has been set to be lower than that of the fan housing 7 as best seen in FIG. 2, and so the surface of the blades 5 is positioned lower than the surface of the housing 7.
The axial height of the fan housing 7 of a conventional axial flow fan is limited to 25 mm with the surface of the blades 5 being necessarily positioned lower than the surface of the fan housing 7. The blades 5 of the conventional axial flow fan undesirably have a simple shape.
In a detailed description, the maximum camber position of each blade 5 of the conventional axial flow fan is set to 0.45, with the camber positions being uniformly distributed on each blade 5 from the blade hub to the blade tip so as to allow the maximum camber position to be positioned close to the blade leading edge. The maximum camber ratio of each blade 5 is 2.0% at the blade hub and 8.0% at the blade tip while accomplishing a linear distribution on the blade 5. Each of the blades 5 is almost free from any sweep angle, while the pitch angle of each blade 5 is rapidly changed from 52xc2x0 at the blade hub to 26xc2x0 at the blade tip having a linear distribution.
Such axial flow fans have been preferably used in electromagnetic induction-heating cookers as shown in FIG. 3 for driving and cooling the cookers.
As shown in FIG. 3, the cooker has an axial flow fan 20 on the bottom wall of its casing. When the axial flow fan 20 is started, atmospheric air is sucked into the casing of the cooker through an inlet grille 21 by the suction force of the axial flow fan 20 and flows under the guide of an air guide 22, thus cooling both a heat dissipating fin 23 and a heating coil 24 prior to being discharged from the casing through an outlet grille 25.
Such axial flow fans 20 may be preferably used in a variety of electronic appliances in addition to the above-mentioned cookers. Particularly, the axial flow fans 20 may be preferably used for cooling the power supply units, lamps and LCD modules of conventional LCD projectors.
The axial flow fans 20, used in electronic appliances, such as LCD projectors and induction-heating cookers, are important elements since the fans 20 drive and cool the appliances. However, the conventional axial flow fans 20 are problematic in that they undesirably generate operational noise, disturbing those around the appliances. Particularly, the operational noise of a conventional axial flow fan 20 installed in an induction-heating cooker forms about 70 percent of the entire operational noise of the cooker. Such an operational noise of the fans 20 causes a serious defect of the electronic appliances using the fans.
That is, the operational performance and operational noise of the axial flow fans directly influence the operational performance and operational noise of appliances using the fans.
The axial height of the blades 5 of a conventional axial flow fan is designed to be lower than that of the fan housing 7. In addition, the blades 5 undesirably have a flat and wide shape with a low camber ratio, a low pitch angle and a low sweep angle. Therefore, the conventional axial flow fan merely generates a reduced air volume while undesirably increasing operational noise.
In a detailed description, when the axial height of the blades 5 is lower than that of the fan housing 7, the radially sucked air volume of the blades 5 is less than the axially sucked air volume of the blades 5. The conventional axial flow fan thus merely generates a reduced air volume while undesirably increasing operational noise.
When the blades 5 have a low sweep angle, they undesirably increase operational noise. When the blades 5 have a low pitch angle, the width of each blade 5 is reduced, thus failing to suck a desired air volume. When the blades 5 have a low camber ratio, it is almost impossible to desirably increase the static pressure of air passing through the fan. This forces the rpm of the fan to be increased so as to accomplish a desired air volume, and finally deteriorates the blowing efficiency of the fan.
Therefore, it is necessary to optimally design the axial heights of both the blades 5 and the fan housing 7, the sweep angle, pitch angle, and camber ratio of the blades 5 so as to accomplish a desired operational effect of electronic appliances using the axial flow fans while accomplishing a desired air volume of the fan in addition to a reduction in operational noise of the fan.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an axial flow fan with a BLDC motor for electronic appliances, which is optimally designed in axial height of both the blades and the fan housing, diameter ratio, the number of blades, camber ratio, pitch angle and sweep angle, thus being improved in blowing operational efficiency in addition to a reduction in operational noise.
In order to accomplish the above object, the primary embodiment of the present invention provides an axial flow fan, comprising a BLDC motor, a hub mounted to the rotating shaft of the motor, a plurality of blades mounted to the hub, and a fan housing covering the blades while holding the motor therein, wherein the blades have an axial height higher than that of the fan housing, with the leading surface of the blades being placed outside the surface of the fan housing at a position higher than the surface of the fan housing by a predetermined projection height, thus increasing an air volume of the fan.
In the primary embodiment, the number of the blades of the axial flow fan is eight, with a diameter ratio of the inner diameter to the outer diameter of the fan being 0.40xcx9c0.45, thus reducing operational noise of the fan. In this embodiment, the blades are designed to have a high sweep angle, a high pitch angle and a high camber ratio.
In the second embodiment, the number of the blades of the axial flow fan is seven, with a diameter ratio of the inner diameter to the outer diameter of the fan being 0.40xcx9c0.43, thus reducing operational noise of the fan. In this embodiment, the blades are designed to have a high sweep angle, a high pitch angle and a high camber ratio.